The goal of this project is to develop gene therapy as a potential treatment for HIV-1 infection. In our early work on anti-HIV gene therapy approaches we reported that retroviral vectors designed to express a variety of gene can inhibit HIV-1 in vitro. Based on our successfully in vitro studies we are now collaborating on a clinical trial to evaluate these approaches in HIV-1 discordant identical twins. A phase I/II pilot study was initiated in August 1996 to evaluate the safety, relative survival, and potential efficacy of infusions of activated, genetically engineered, syngeneic CD4+ T lymphocytes obtained from HIV seronegative identical twins. T cells from each seronegative twin were obtained by apheresis, enriched for CD4+ cells, induced to polyclonal proliferation with anti-CD3 and rIL-2 stimulation, transduced with a control (Neo-containing) retroviral vector and up to two additional retroviral vectors containing potentially therapeutic genes (antisense TAR and/or transdominant Rev). The engineered T cell populations were expanded and then infused into the seropositive twins (between 4-20 X 109 CD4+ T-cells were administered). In vitro gene transfer efficiencies ranged from 1.0% (for a low titer PA317 packaged vector) to 40% (for a PG13 packaged vector). 8 patients have been treated to date with a total of 15 separate infusions (each patient will receive 2 infusions of different combinations of vectors). The relative survival of the uniquely engineered T cells is being monitored by vector-specific PCR. Initial results from this study demonstrate good levels of gene transfer and persistence of vector signals for at least 30 weeks post infusion. The amount of engineered CD4+ cells detected in total PBMC correlated with the amount of in vitro gene transfer and varied between 2.0% to 0.1% of total PBMC immediately following infusion. In most treatment cycles, vector signal gradually declined 1 log over the next 4-8 weeks and then stabilized for varying lengths of time. The ratio of therapeutic v ector/control vector for the majority patients studied is slightly increased in vivo in comparison to the in vitro transduced lymphocyte populations. Transient increases in CD4 counts were seen in all patients following one or more cell infusions and persisted from 4 to 28 weeks.